Automated transmissions are known, in which an internal combustion engine directly drives a torque converter as a start up element, which converts the input torque and transfers it to the automated transmission. Torque converters are thus configured in hydrodynamic construction with a pump shell directly driven by the internal combustion engine and with a turbine shell driven by the pump shell through an operating means, which turbine shell is coupled to the transmission on the output side. In order to augment the torque, a stator or a stator shell is fixed to the housing by means of a one-way clutch, which stator is supported at the housing at low speeds of the pump shell and transmits an additional torque into the operating means, and thus eventually to the turbine shell.
Due to the non-form locked connection of the turbine shell to the pump shell, the motor vehicle can be held standing still with a gear shifted and with the internal combustion engine running at idle. The idle torque occurring due to the standstill conversion can be held by the operating brake or by the parking brake. When the brake is released, the motor vehicle creeps independently. Thus the gearing of the start-up process is adapted to the characteristics of the torque converter in order to achieve a predetermined creeping velocity.
The characteristic, depends, for example, on the external shape, the type of blading of pump and turbine shells, the operating means used and similar factors. A difference is being made between so-called hard torque converters and soft torque converters, wherein a soft torque converter comprises a flat torque characteristic over the speed of the pump shell and a hard torque converter comprises a steeper torque characteristic over the speed of the pump shell. This yields a comparatively small efficiency for soft torque converters compared to hard torque converters.
In order to save fuel, transmissions are to be configured with a highest gear, which is configured as so-called overdrive, thus with a long gearing. This means that due to the limited gear ratio spread, in particular in planetary transmissions, the first gear, thus the start-up gear is also configured with a comparatively long gearing. In case of a soft torque converter, this leads to undesirably slow acceleration values of the motor vehicle, and in case of hard torque converters, this leads to unacceptably high creeping velocities in the range of the idle speed of the internal combustion engine. Furthermore, it is desirable in order to save fuel to avoid the energy consumption created by the converter slippage, when the internal combustion engine idles and the motor vehicle is stopped.